There is a strong impetus for developing regenerative absorption processes for SO2 recovery from gas flows. The term “regenerative” in this case usually implies that the active absorption solution is regenerated, and thus made ready for reuse. At the same time, the absorbed SO2 is set free in a concentrated, useful form. Such regenerative processes are especially attractive for treating large gas flows with high SO2 concentrations, when the otherwise commonly used lime/limestone based processes are less suitable. SO2 recovery is also especially attractive when there is a local demand for SO2, for example for sulphuric acid production, or when there is available a Claus plant for producing elemental sulphur from H2S, such as in oil refineries.
Important problems with regenerative SO2-processes are:                Insufficient chemical stability of the active absorbent, leading to too high reagent consumption.        Insufficient pre-cleaning of the feed gas, which again leads to losses of reagent solution.        The formation of unwanted sulphur compounds by unwanted side reactions, especially sulphate formation by oxidation caused by oxygen being absorbed, from the feed gas.        Under certain conditions, dis-proportioning reactions may occur, producing, for example, thiosulphate.        
The unwanted products accumulate in the buffer solution, and have to be removed, in order to avoid operation disturbances caused by precipitation through super-saturation. SO2 oxidation first leads to sulphuric acid, which must be neutralized by addition of a base, for example NaOH, in order to counteract acidification of the buffer. Then sodium sulphate forms.
One possibility of avoiding super-saturation of sodium sulphate is to drain a sufficient stream of buffer slurry from the evaporator. However, this may lead to a substantial consumption of valuable chemicals, and may—in addition—represent a disposal problem.